1. Field of the Invention
This invention relates to the upgrading of hydrocarbon oil feedstock to remove undesirable sulfur- and nitrogen-containing compounds using solid adsorbents.
2. Description of Related Art
Various references disclose processes for the direct separation of sulfur compounds from naphtha and diesel feedstreams using membrane separation technology or solid adsorption methods. The following are representative of certain process treatment steps.
In U.S. Pat. No. 6,524,469, a heavy oil conversion process is disclosed in which the heavy oil feed is first thermally cracked using visbreaking or hydrovisbreaking technology to produce a product that is lower in molecular weight and boiling point than the feed. The product is then deasphalted using an alkane solvent at a solvent to feed ratio of less than 2. The solvent and the deasphalted oil are separated from the asphaltenes through the use of a two-stage membrane separation system.
U.S. Pat. No. 6,736,961 describes a process for removing sulfur from a hydrocarbon employing with the use of a solid membrane. A relatively large quantity of feed stream containing liquid hydrocarbons and sulfur species is conveyed past one side of the solid membrane, while a relatively small quantity of a sweep stream is conveyed past the opposite side of the solid membrane. The feed sulfur species is transported in a permeate from the feed-stream through the solid membrane to the sweep stream. The feed stream is converted to a relatively large quantity of a substantially sulfur-free retentate stream containing a primary hydrocarbon product, while the sweep stream combines with the permeate to produce a relatively small quantity of a sulfur-enriched stream, which is amenable to further processing such as hydrotreating.
U.S. Pat. No. 6,896,796 describes a membrane process for the removal of sulfur species from a naphtha feed, in particular, FCC light cat naphtha. The process involves contacting a naphtha feed stream with a membrane having sufficient flux and selectivity to separate a sulfur deficient retentate fraction from a sulfur enriched permeate fraction, preferably, under pervaporation conditions. Sulfur deficient retentate fractions are useful directly into the gasoline pool. Sulfur-enriched permeate fractions are rich in sulfur containing aromatic and nonaromatic hydrocarbons and are further treated with conventional sulfur removal technologies, e.g. hydrotreating, to reduce sulfur content. The process of the invention provides high quality naphtha products having reduced sulfur content and a high content of olefin compounds.
In published patent application US2002/0111524, a process is disclosed for the separation of sulfur compounds from a hydrocarbon mixture using a membrane. Preferred hydrocarbon mixtures are oil refining fractions such as light cracked naphtha. Membranes are composed of either ionic or non-ionic materials and preferentially permeate sulfur compounds over other hydrocarbons. A single or multi-stage membrane system separates the hydrocarbon mixture into a sulfur-rich fraction and a sulfur-lean fraction. The sulfur-lean fraction may be used in fuel mixtures and the sulfur-rich fraction may be further treated for sulfur reduction.
U.S. Pat. No. 5,643,442 describes a process for distillate or hydrotreated distillate effluents, where an aromatics-rich permeate and an aromatics lean retentate are separated by use of a permselective membrane. The aromatic rich permeate is sent to a hydrotreater for further processing, thereby increasing the quantity of reduced aromatics in the product.
U.S. Pat. No. 5,114,689 describes a process utilizing a primary adsorption bed containing a regenerable, physical adsorbent and an auxiliary sorption bed containing a chemisorbent for the removal of sulfur compounds from a fluid stream, which process purports to provide higher yields, higher purity and lower operating costs.
In published patent application US2002/0139719, methods for the separation of sulfur compounds from a liquid hydrocarbon mixture using a hydrophilic, non-ionic membrane are disclosed. The membrane can also be composed of water-soluble material. Preferred membranes include polyvinylpyrrolidone and cellulose triacetate membranes. The liquid hydrocarbon mixture can include a light cracked naphtha.
In U.S. Pat. No. 6,187,987, perm selective separation of aromatic hydrocarbons from non-aromatic hydrocarbons in a feed stream is accomplished using improved asymmetric membranes. The preferred membranes are fashioned from a polyimide and conditioned with lubricating oil. Feed streams containing a mixture of aromatic and non-aromatic hydrocarbons are contacted with the dense active layer side of the polyimide membrane under a pressure and temperature sufficient to selectively permeate the desired aromatic hydrocarbon.
U.S. Pat. No. 6,024,880 discloses a method suitable for treating used oil to remove contaminants including ash and color contaminants in order to provide a purified oil product. The method utilizes a porous inorganic membrane module having a high pressure side and a low pressure side. The oil to be treated is introduced to the high pressure side of the membrane module to provide an oil permeate on the low pressure side and an ash rich concentrate on the high pressure side thereby separating ash in the oil from the oil permeate. Thereafter, the oil permeate is contacted with an adsorbent to remove color and odor to provide a purified oil product. The spent adsorbent can be regenerated and reused.
In U.S. Pat. No. 5,082,987, a method and apparatus are described whereby a caustic-treated hydrocarbon feed mixture having a contaminating concentration of water and sulfur compounds is treated by separating the hydrocarbon feed into a first stream and a second stream. The first stream is contacted with an adsorbent material to produce a reactor feed stream having a significant reduction in the concentration of the contaminating water and sulfur compounds. The reactor feed stream is thereafter contacted in the presence of hydrogen under suitable isomerization conditions with an isomerization catalyst to produce an isomerate product.
Thus, while membrane technology and adsorbent technology have been separately applied to provide cleaner fuels, no disclosure has been found suggesting that both technologies be combined to separate the impurities from a hydrocarbon oil.
It is therefore an object of the present invention to provide an improved process for upgrading a hydrocarbon oil feedstream by removing and reducing the amounts of undesired sulfur- and nitrogen-containing compounds.
Another object of the invention is to provide such a process that is carried out under mild reaction conditions and utilizing conventional apparatus.